Wikipedia:Category intersection/Separate intersection space

This is one variant for a proposed category intersection feature.

For mockups, see:
 * Intersection:Actor::American people::People of African descent
 * Intersection:Writers::People by nationality

Getting to intersections
In this variant, intersections have their own namespace and are reached:
 * 1) By typing the URL of the intersection.
 * 2) By typing the name of the intersection in the "Search box" and clicking on "Go".
 * 3) By creating a link to the intersection on a page and then clicking on the link (this will be useful for discussions and for adding traversal links from categories to intersections).
 * 4) By selecting categories to intersection from those listed at the bottom of article pages.
 * 5) By selecting other categories to intersect from an intersection selection table display on another intersection page.

The most frequent path to "intersection space" will likely be from the selection mechanism presented at the bottom of each article. The list of categories includes a checkbox for each category and a link to go to the intersection of the selected categories. The destination page is a page in intersection space with a top portion very similar to a category page displaying any previously saved annotations, plus an automatically generated list of categories and articles "in" the intersection. The primary difference between this proposal and the others is what's at the bottom of the intersection page. In this proposal, the bottom of each intersection page displays an automatically generated intersection selection table allowing the user to traverse to other related intersections (as shown in the mockup).

Intersection categories
Intersections selected from articles will generally correspond to what today would be an "intersection category", like category:African-American actors. A mockup of what the corresponding intersection page might look like is at Category intersection/Rick's mockup/African-American actors. Note that the top section looks nearly identical to the category, but instead of relying on adding articles to category:African-American actors the articles listed would be those included in all three of the primary categories. The traversal within this intersection would be just like the traversal within an existing category, with next and previous links to the next set of 200 members. This means the URL for an intersection must support a  parameter, which also means a template like template:CategoryTOC could be added to "large" intersections.

Traversal
In the current system, traversal from categories is by "subcategories" ("down" the hierarchy) or by "parent" categories ("up" the hierarchy). For example, from category:African-American actors there are no subcategories but traversal "up" to category:American actors by ethnicity or category:African Americans is supported (because category:African-American actors is in these categories). There are no existing subcategories for category:African-American film actors or category:African-American stage actors, so there is no way to traverse to these categories. The intersection selection table, as shown in the mockup allows a user to traverse directly to intersections corresponding to these subcategories, and any other combination of subcats or parent cats of any of the intersected categories. In this proposal category:American actors by ethnicity and category:African Americans would also both be intersections, specifically intersection:American people::Actors::People by ethnic or national descent and intersection:American people::People of African descent. These intersections, as well as many more, are available from the intersection selection table, without anyone explicitly adding them as a "parent".

Index categories
There are currently numerous "X by Y" index categories allowing traversal within the category namespace. Categories must be manually added to these intersection categories for them to function. For example, Category:Writers by nationality is manually populated by adding this category as a "parent" category to a specific Category:Fooian writers category (for example, Category:American writers). In this proposal, these index categories can be replaced by automatically generated intersections. For example, Category:Writers by nationality would be replaced with Intersection:Writers::People by nationality, see mockup. This "index intersection" would be accessible from the index selection table of any "Fooian writers" intersection (again, without anyone explicitly adding it as a "parent") because category:people by nationality would be a parent category of category:Fooian people. This mockup shows two different alternatives to the issue of how to handle an intersection of a category that has a large number of subcategories (such as category:people by nationality).

Summary
Assuming an acceptable method for handling a large number of subcategories in an index selection table is developed, this variant provides an extremely powerful mechanism allowing both "intersection categories" (like Category:African-American actors) as well as "index categories" (like Category:Writers by nationality) to be replaced with intersections. In fact, implementing this variant and simply deleting all the "intersection" and "index" categories leads to nearly equivalent operation with thousands fewer categories.